The present invention relates generally to drive mechanisms for work transfer apparatus and more particularly to such drive mechanisms incorporating both a stationary sun gear and a revolving and rotating planet gear operative to provide a transfer motion characterized by substantially zero acceleration and jerk at both beginning and end of the transfer travel.
Transfer apparatus of various types have long been in use in conjunction with various types of manufacturing and assembly operations in order to advance workpieces between work stations as well as into and out of various types of machinery. Numerous types of drive systems have been developed over the years in order to accomplish this work transfer operation in a rapid and efficient manner. Such drive systems have employed a variety of different combinations of barrel cams, bell cranks, lever arms, or scotch yoke connections and the like. Typically such drive systems are designed to effect operative transfer movement in a single plane and must be able to provide periods of dwell at both beginning and ends of the operational cycle with intermediate periods of acceleration/deceleration.
It is also highly desirable to provide drive systems for such transfer apparatus which are able to smoothly reciprocate the workpieces into and out of the work stations without subjecting either the workpiece or the associated apparatus to shocks or jerk resulting from sudden acceleration or deceleration as the workpiece is moved from or to a stationary position. This is particularly important with regard to such transfer apparatus which are designed for use in assembly or precision machining operations wherein the jerk may dislodge or otherwise dislocate parts being processed although it is desirable to avoid such jerk in all applications because of the adverse effect resulting from subjecting the entire drive train to the stress and strain associated therewith.
It should be noted that as used herein the term "jerk" is defined as the third derivative of displacement with respect to time or the second derivative of velocity with respect to time or the first derivative of acceleration with respect to time.
In addition to reducing or eliminating jerk in such transfer apparatus both at the beginning and end of operational cycles, it is also desirable to design such apparatus to be able to reciprocate the workpiece into and out of the work station as rapidly as possible because this transfer represents lost production time. Also, in order to avoid excessive downtime as well as high maintenance costs, it is highly desirable to design such apparatus as simply as possible with a minimum number of moving parts. Coupled with the desire to maintain the design as simple as possible while still accommodating the other operational aspects required is the desirability to enable the apparatus to be easily fabricated at relatively low cost without sacrificing reliability. While previous transfer drive arrangements have been able to achieve differing measures of success in meeting the above conflicting objectives, none of them have been totally effective in providing a completely acceptable transfer drive assembly.
The present invention, however, provides a transfer drive mechanism which utilizes a gearing system constructed so as to provide a transfer motion in which the workpieces are subjected to substantially zero jerk at either end of the transfer cycle and experience a smoothly but rapidly increasing rate of acceleration/deceleration. The drive mechanism is relatively simple in construction comprising a stationary sun gear and a planet gear in meshing engagement therewith adapted to be driven in revolution around the sun gear and rotated thereby. An eccentric follower pin is provided on the planet gear to which suitable linkage or the like is connected whereby movement of the eccentric follower may be transferred to the workpiece supporting portion of the work transfer apparatus. The diameter of the planet gear and sun gear are selected in accordance with the relative positioning of the eccentric follower pin and the desired distance of travel so as to provide a desired transfer movement of the workpiece characterized by substantially zero acceleration/deceleration and jerk at both the beginnings and end of the transfer motion cycle.
The drive apparatus of the present invention not only substantially provides these highly desirable movement characteristics whereby workpieces may be rapidly and effectively transferred without being jarred out of position but does so with a relatively uncomplicated straightforward mechanism that utilizes relatively few parts and hence may be easily serviced and maintained with a minimum of downtime. Additionally, because the drive apparatus requires relatively few moving parts, it offers excellent reliability.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.